The invention is especially concerned with an apparatus of the above mentioned type in which the clamp bushing is of the known type which is formed with a thin inner sleeve or inner wall, a solid outer sleeve, and a plastic or hydraulic pressure medium enclosed between said sleeves, and in which said this inner sleeve is arranged to both centre and clamp connecting a rotating tool or a work piece when the hydraulic pressure medium is pressurized, and in which the chuck is formed as an integral unit with the mounting cone shaft or with the machine spindle.
Special advantages are achieved in such an apparatus, in which the hydraulic clamp bushing is joined with the mounting cone shaft or the machine spindle by a welding and soldering method executed so that an optimum little amount of heat is developed thereby preventing a damage of existing heat treatments of the chuck and/or so as to prevent a damage of the hydraulic pressure medium of the hydraulic clamp bushing. Useful joining methods are for instance electron beam welding or laser welding or laser soldering. In such known apparatus both the hydraulic clamp bushing part and the mounting cone part or the machine spindle part generally have to be finally machined after after the welding or soldering process, so that the cone or the spindle and the clamp connection bore of the clamp bushing get an accurate radial, rotary precision.
In rotary machining of materials, like in milling, turning, drilling, threading, reaming, grinding etc. of various materials it has, since long, been practice to make use of machine tools having a spindle, or several spindles, of the rotary type, in which chucks can be mounted. Machine tools or work pieces are clamped to said chucks, either by being clamp connected by means of radially outwards acting clamp means, or most commonly by being clamped by means of radially inwards acting clamp means.
The chucks of said known apparatus generally have been formed with a conical shaft having a clamp means at the end thereof, namely the actual clamp chuck, in which the tools or the work pieces are clamped. The conical shaft of the chuck, which is the actual mounting cone, is mounted in the rotary spindle of the working machine by being pressed into an inner conical recess of said spindle.
The clamp means for the tool can be a mechanical structure having several metal elements which are, in common, screwed radially inwards towards the centre thereof, or eventually radially outwards, and which thereby clamp the tool or the work piece in the chuck.
The said known clamping means normally gives an acceptable precision for machining, but in same cases it may be desired to foresee a higher precision in the machining. This has been made possible by means of chucks developed during the latest years, which chucks are formed with a hydraulic clamp portion of the above mentioned type having an inner and/or an outer thin wall or sleeve and inside said this wall an annular space which is filled with a plastic or hydraulic pressure medium which, upon pressurization, brings the said thin wall to expand radially inwards (and/or radially outwards) thereby centering and clamp connecting the tool or the work piece to the chuck. Correctly designed such hydraulic clamping parts or chucks provide a very accurate radial rotary precision for the clamped tool or work piece. By providing a high rotary precision it is possible to more rationally utilize the machines and the tools, for instance by using higher feeding speeds, or by foreseeing a higher precision and a better quality of the machined surfaces.
However, also in chucks having a hydraulic clamping means the above mentioned method of joining the conical shaft of the chuck with the conical recess of the machine spindle may cause imperfect so called "radial rotary precision" for the tool which is clamped in the chuck. Since the clamping means necessarily is mounted at the end of the chuck cone, and since further said chuck cone must have a certain axial length for making it possible to steadily connect the chuck to the machine spindle the distance between the clamped tool and the bearings of the machine spindle may sometimes be relatively great, and this reduces the working precision and unneccesarily stresses the bearings of the machine spindle and may cause hard wear of said bearings.
Attempts have been made to solve said last mentioned problem by mounting of the clamp part directly on the machine spindle by means screw or bolt joints, but also such connection means involve remaining sources of errors in the joint between the clamp part and the machine spindle. Also, there is a need for a relatively large space for the screw joint between the clamp part and the machine spindle, and the clamp part may become unneccessarily large and heavy.